The present invention relates to the field of electrical connectors, particularly internal electrical connectors for coaxial cables. The preferred electrical connectors are particularly well suited for use in difficult environments wherein it is desirable to electrically connect inside a coaxial cable without the normal means available such as BNC, RCA, SMA, SMB, and TNC type coaxial connectors. One such application is in data transmission systems suitable for downhole environments, such as along a drill string used in oil and gas exploration or along the casings and other equipment used in oil and gas production.
The goal of accessing data from a drill string has been expressed for more than half a century. As exploration and drilling technology has improved, this goal has become more important in the industry for successful oil, gas, and geothermal well exploration and production. For example, to take advantage of the several advances in the design of various tools and techniques for oil and gas exploration, it would be beneficial to have real time data such as temperature, pressure, inclination, salinity, etc. Several attempts have been made to devise a successful system for accessing such drill string data. One such system is disclosed in co-pending U.S. application Ser. No. 09/909,469 (also published as PCT Application WO 02/06716) which is assigned to the same assignee as the present invention.
A typical drill string is comprised of several hundred sections of downhole tools such as pipe, heavy weight drill pipe, jars, drill collars, etc. Therefore it is desirable to locate the electrical system within each downhole tool and then make electrical connections when the sections are joined together. One problem for such systems is that the downhole environment is quite harsh. The drilling mud pumped through the drill string is abrasive, slightly basic or alkaline, and typically has a high salt content. In addition, the downhole environment typically involves high pressures and temperatures. Moreover, heavy grease is typically applied at the joints between pipe sections. Consequently, the reliance on an electrical contact between joined pipe sections is typically fraught with problems.
One solution to this problem common in the drilling industry is mud pulse telemetry. Rather than using electrical connections, mud pulse telemetry transmits information in the form of pressure pulses through drilling mud circulating through the drill string and borehole. However, data rates of mud pulse telemetry are very slow compared to data rates needed to provide real-time data from downhole tools.
For example, mud pulse telemetry systems often operate at data rates less than 10 bits per second. Since drilling equipment is often rented and very expensive, even slight mistakes incur substantial expense. Part of the expense can be attributed to time-consuming operations that are required to retrieve downhole data or to verify low-resolution data transmitted to the surface by mud pulse telemetry. Often, drilling or other procedures are halted while crucial data is gathered.
Moreover, the harsh working environment of downhole tools may cause damage to data transmission elements. Furthermore, since many downhole tools are located beneath the surface of the ground, replacing or servicing data transmission tools may be costly, impractical, or impossible. Thus, robust and environmentally hardened data transmission tools are needed to transmit information between downhole tools.
Downhole data transmission systems require reliable and robust electrical connections to insure that quality data signals are received at the top of the borehole.